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 .. _reST primer:
 ===========
 reST primer
 ===========
 .. sidebar:: KISS_ and readability_
    Instead of defining more and more roles, we at searx encourage our
    contributors to follow principles like KISS_ and readability_.
 We at searx are using reStructuredText (aka reST_) markup for all kind of
 documentation, with the builders from the Sphinx_ project a HTML output is
 generated and deployed at :docs:`github.io <.>`.  For build prerequisites read
 :ref:`docs build`.
 The source files of Searx's documentation are located at :origin:`docs`.  Sphinx
 assumes source files to be encoded in UTF-8 by defaul.  Run :ref:`make docs-live
 <make docs-live>` to build HTML while editing.
 .. sidebar:: Further reading
    - Sphinx-Primer_
    - `Sphinx markup constructs`_
    - reST_, docutils_, `docutils FAQ`_
    - Sphinx_, `sphinx-doc FAQ`_
    - `sphinx config`_, doctree_
    - `sphinx cross references`_
    - linuxdoc_
    - intersphinx_
    - sphinx-jinja_
    - `Sphinx's autodoc`_
    - `Sphinx's Python domain`_, `Sphinx's C domain`_
    - SVG_, ImageMagick_
    - DOT_, `Graphviz's dot`_, Graphviz_
 .. contents:: Contents
    :depth: 3
    :local:
    :backlinks: entry
 Sphinx_ and reST_ have their place in the python ecosystem.  Over that reST is
 used in popular projects, e.g the Linux kernel documentation `[kernel doc]`_.
 .. _[kernel doc]: https://www.kernel.org/doc/html/latest/doc-guide/sphinx.html
 .. sidebar:: Content matters
    The readability_ of the reST sources has its value, therefore we recommend to
    make sparse usage of reST markup / .. content matters!
 **reST** is a plaintext markup language, its markup is *mostly* intuitive and
 you will not need to learn much to produce well formed articles with.  I use the
 word *mostly*: like everything in live, reST has its advantages and
 disadvantages, some markups feel a bit grumpy (especially if you are used to
 other plaintext markups).
 Soft skills
 ===========
 Before going any deeper into the markup let's face on some **soft skills** a
 trained author brings with, to reach a well feedback from readers:
 - Documentation is dedicated to an audience and answers questions from the
   audience point of view.
 - Don't detail things which are general knowledge from the audience point of
   view.
 - Limit the subject, use cross links for any further reading.
 To be more concrete what a *point of view* means.  In the (:origin:`docs`)
 folder we have three sections (and the *blog* folder), each dedicate to a
 different group of audience.
 User's POV: :origin:`docs/user`
   A typical user knows about search engines and might have heard about
   meta crawlers and privacy.
 Admin's POV: :origin:`docs/admin`
   A typical Admin knows about setting up services on a linux system, but he does
   not know all the pros and cons of a searx setup.
 Developer's POV: :origin:`docs/dev`
   Depending on the readability_ of code, a typical developer is able to read and
   understand source code.  Describe what a item aims to do (e.g. a function).
   If the chronological order matters, describe it.  Name the *out-of-limits
   conditions* and all the side effects a external developer will not know.
 .. _reST inline markup:
 Basic inline markup
 ===================
 .. sidebar:: Inline markup
    - :ref:`reST roles`
    - :ref:`reST smart ref`
 Basic inline markup is done with asterisks and backquotes.  If asterisks or
 backquotes appear in running text and could be confused with inline markup
 delimiters, they have to be escaped with a backslash (``\*pointer``).
 .. table:: basic inline markup
    :widths: 4 3 7
    ================================================ ==================== ========================
    description                                      rendered             markup
    ================================================ ==================== ========================
    one asterisk for emphasis                        *italics*            ``*italics*``
    two asterisks for strong emphasis                **boldface**         ``**boldface**``
    backquotes for code samples and literals         ``foo()``            ````foo()````
    quote asterisks or backquotes                    \*foo is a pointer   ``\*foo is a pointer``
    ================================================ ==================== ========================
 .. _reST basic structure:
 Basic article structure
 =======================
 The basic structure of an article makes use of heading adornments to markup
 chapter, sections and subsections.
 .. _reST template:
 reST template
 -------------
 reST template for an simple article:
 .. code:: reST
     .. _doc refname:
     ==============
     Document title
     ==============
     Lorem ipsum dolor sit amet, consectetur adipisici elit ..  Further read
     :ref:`chapter refname`.
     .. _chapter refname:
     Chapter
     =======
     Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut
     aliquid ex ea commodi consequat ...
     .. _section refname:
     Section
     -------
     lorem ..
     .. _subsection refname:
     Subsection
     ~~~~~~~~~~
     lorem ..
 Headings
 --------
 #. title - with overline for document title:
   .. code:: reST
     ==============
     Document title
     ==============
 #. chapter - with anchor named ``anchor name``:
    .. code:: reST
       .. _anchor name:
       Chapter
       =======
 #. section
    .. code:: reST
       Section
       -------
 #. subsection
    .. code:: reST
       Subsection
       ~~~~~~~~~~
 Anchors & Links
 ===============
 .. _reST anchor:
 Anchors
 -------
 .. _ref role:
    https://www.sphinx-doc.org/en/master/usage/restructuredtext/roles.html#role-ref
 To refer a point in the documentation a anchor is needed.  The :ref:`reST
 template <reST template>` shows an example where a chapter titled *"Chapters"*
 gets an anchor named ``chapter title``.  Another example from *this* document,
 where the anchor named ``reST anchor``:
 .. code:: reST
    .. _reST anchor:
    Anchors
    -------
    To refer a point in the documentation a anchor is needed ...
 To refer anchors use the `ref role`_ markup:
 .. code:: reST
    Visit chapter :ref:`reST anchor`.  Or set hyperlink text manualy :ref:`foo
    bar <reST anchor>`.
 .. admonition:: ``:ref:`` role
    :class: rst-example
    Visist chapter :ref:`reST anchor`.  Or set hyperlink text manualy :ref:`foo
    bar <reST anchor>`.
 .. _reST ordinary ref:
 Link ordinary URL
 -----------------
 If you need to reference external URLs use *named* hyperlinks to maintain
 readability of reST sources.  Here is a example taken from *this* article:
 .. code:: reST
    .. _Sphinx Field Lists:
       https://www.sphinx-doc.org/en/master/usage/restructuredtext/field-lists.html
    With the *named* hyperlink `Sphinx Field Lists`_, the raw text is much more
    readable.
    And this shows the alternative (less readable) hyperlink markup `Sphinx Field
    Lists
    <https://www.sphinx-doc.org/en/master/usage/restructuredtext/field-lists.html>`__.
 .. admonition:: Named hyperlink
    :class: rst-example
    With the *named* hyperlink `Sphinx Field Lists`_, the raw text is much more
    readable.
    And this shows the alternative (less readable) hyperlink markup `Sphinx Field
    Lists
    <https://www.sphinx-doc.org/en/master/usage/restructuredtext/field-lists.html>`__.
 .. _reST smart ref:
 Smart refs
 ----------
 With the power of sphinx.ext.extlinks_ and intersphinx_ referencing external
 content becomes smart.
 .. table:: smart refs with sphinx.ext.extlinks_ and intersphinx_
    :widths: 4 3 7
    ========================== ================================== ====================================
    refer ...                  rendered example                   markup
    ========================== ================================== ====================================
    :rst:role:`rfc`            :rfc:`822`                         ``:rfc:`822```
    :rst:role:`pep`            :pep:`8`                           ``:pep:`8```
    sphinx.ext.extlinks_
    --------------------------------------------------------------------------------------------------
    project's wiki article     :wiki:`Offline-engines`            ``:wiki:`Offline-engines```
    to docs public URL         :docs:`dev/reST.html`              ``:docs:`dev/reST.html```
    files & folders origin     :origin:`docs/dev/reST.rst`        ``:origin:`docs/dev/reST.rst```
    pull request               :pull:`1756`                       ``:pull:`1756```
    patch                      :patch:`af2cae6`                   ``:patch:`af2cae6```
    PyPi package               :pypi:`searx`                      ``:pypi:`searx```
    manual page man            :man:`bash`                        ``:man:`bash```
    intersphinx_
    --------------------------------------------------------------------------------------------------
    external anchor            :ref:`python:and`                  ``:ref:`python:and```
    external doc anchor        :doc:`jinja:templates`             ``:doc:`jinja:templates```
    python code object         :py:obj:`datetime.datetime`        ``:py:obj:`datetime.datetime```
    flask code object          :py:obj:`flask.Flask`              ``:py:obj:`flask.Flask```
    ========================== ================================== ====================================
 Intersphinx is configured in :origin:`docs/conf.py`:
 .. code:: python
     intersphinx_mapping = {
         "python": ("https://docs.python.org/3/", None),
         "flask": ("https://flask.palletsprojects.com/", None),
         "jinja": ("https://jinja.palletsprojects.com/", None),
         "linuxdoc" : ("https://return42.github.io/linuxdoc/", None),
         "sphinx" : ("https://www.sphinx-doc.org/en/master/", None),
     }
 To list all anchors of the inventory (e.g. ``python``) use:
 .. code:: sh
    $ python -m sphinx.ext.intersphinx https://docs.python.org/3/objects.inv
 Literal blocks
 ==============
 The simplest form of :duref:`literal-blocks` is a indented block introduced by
 two colons (``::``).  For highlighting use :dudir:`highlight` or :ref:`reST
 code` directive.  To include literals from external files use
 :rst:dir:`literalinclude` or :ref:`kernel-include <kernel-include-directive>`
 directive (latter one expands environment variables in the path name).
 .. _reST literal:
 ``::``
 ------
 .. code:: reST
    ::
      Literal block
    Lorem ipsum dolor::
      Literal block
    Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
    eirmod tempor invidunt ut labore ::
      Literal block
 .. admonition:: Literal block
    :class: rst-example
    ::
      Literal block
    Lorem ipsum dolor::
      Literal block
    Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
    eirmod tempor invidunt ut labore ::
      Literal block
 .. _reST code:
 ``code-block``
 --------------
 .. _pygments: https://pygments.org/languages/
 .. sidebar:: Syntax highlighting
    is handled by pygments_.
 The :rst:dir:`code-block` directive is a variant of the :dudir:`code` directive
 with additional options.  To learn more about code literals visit
 :ref:`sphinx:code-examples`.
 .. code-block:: reST
    The URL ``/stats`` handle is shown in :ref:`stats-handle`
    .. code-block:: Python
       :caption: python code block
       :name: stats-handle
       @app.route('/stats', methods=['GET'])
       def stats():
           """Render engine statistics page."""
           stats = get_engines_stats()
           return render(
               'stats.html'
               , stats = stats )
 .. code-block:: reST
 .. admonition:: Code block
    :class: rst-example
    The URL ``/stats`` handle is shown in :ref:`stats-handle`
    .. code-block:: Python
       :caption: python code block
       :name: stats-handle
       @app.route('/stats', methods=['GET'])
       def stats():
           """Render engine statistics page."""
           stats = get_engines_stats()
           return render(
               'stats.html'
               , stats = stats )
 Unicode substitution
 ====================
 The :dudir:`unicode directive <unicode-character-codes>` converts Unicode
 character codes (numerical values) to characters.  This directive can only be
 used within a substitution definition.
 .. code-block:: reST
    .. |copy| unicode:: 0xA9 .. copyright sign
    .. |(TM)| unicode:: U+2122
    Trademark |(TM)| and copyright |copy| glyphs.
 .. admonition:: Unicode
    :class: rst-example
    .. |copy| unicode:: 0xA9 .. copyright sign
    .. |(TM)| unicode:: U+2122
    Trademark |(TM)| and copyright |copy| glyphs.
 .. _reST roles:
 Roles
 =====
 .. sidebar:: Further reading
    - `Sphinx Roles`_
    - :doc:`sphinx:usage/restructuredtext/domains`
 A *custom interpreted text role* (:duref:`ref <roles>`) is an inline piece of
 explicit markup.  It signifies that that the enclosed text should be interpreted
 in a specific way.
 The general markup is one of:
 .. code:: reST
    :rolename:`ref-name`
    :rolename:`ref text <ref-name>`
 .. table:: smart refs with sphinx.ext.extlinks_ and intersphinx_
    :widths: 4 3 7
    ========================== ================================== ====================================
    role                       rendered example                   markup
    ========================== ================================== ====================================
    :rst:role:`guilabel`       :guilabel:`&Cancel`                ``:guilabel:`&Cancel```
    :rst:role:`kbd`            :kbd:`C-x C-f`                     ``:kbd:`C-x C-f```
    :rst:role:`menuselection`  :menuselection:`Open --> File`     ``:menuselection:`Open --> File```
    :rst:role:`download`       :download:`this file <reST.rst>`   ``:download:`this file <reST.rst>```
    math_                      :math:`a^2 + b^2 = c^2`            ``:math:`a^2 + b^2 = c^2```
    :rst:role:`ref`            :ref:`svg image example`           ``:ref:`svg image example```
    :rst:role:`command`        :command:`ls -la`                  ``:command:`ls -la```
    :durole:`emphasis`         :emphasis:`italic`                 ``:emphasis:`italic```
    :durole:`strong`           :strong:`bold`                     ``:strong:`bold```
    :durole:`literal`          :literal:`foo()`                   ``:literal:`foo()```
    :durole:`subscript`        H\ :sub:`2`\ O                     ``H\ :sub:`2`\ O``
    :durole:`superscript`      E = mc\ :sup:`2`                   ``E = mc\ :sup:`2```
    :durole:`title-reference`  :title:`Time`                      ``:title:`Time```
    ========================== ================================== ====================================
 Figures & Images
 ================
 .. sidebar:: Image processing
    With the directives from :ref:`linuxdoc <linuxdoc:kfigure>` the build process
    is flexible.  To get best results in the generated output format, install
    ImageMagick_ and Graphviz_.
 Searx's sphinx setup includes: :ref:`linuxdoc:kfigure`.  Scaleable here means;
 scaleable in sense of the build process.  Normally in absence of a converter
 tool, the build process will break.  From the authors POV it’s annoying to care
 about the build process when handling with images, especially since he has no
 access to the build process.  With :ref:`linuxdoc:kfigure` the build process
 continues and scales output quality in dependence of installed image processors.
 If you want to add an image, you should use the ``kernel-figure`` (inheritance
 of :dudir:`figure`) and ``kernel-image`` (inheritance of :dudir:`image`)
 directives.  E.g. to insert a figure with a scaleable image format use SVG
 (:ref:`svg image example`):
 .. code:: reST
    .. _svg image example:
    .. kernel-figure:: svg_image.svg
       :alt: SVG image example
       Simple SVG image
     To refer the figure, a caption block is needed: :ref:`svg image example`.
 .. _svg image example:
 .. kernel-figure:: svg_image.svg
    :alt: SVG image example
    Simple SVG image.
 To refer the figure, a caption block is needed: :ref:`svg image example`.
 DOT files (aka Graphviz)
 ------------------------
 With :ref:`linuxdoc:kernel-figure` reST support for **DOT** formatted files is
 given.
 - `Graphviz's dot`_
 - DOT_
 - Graphviz_
 A simple example is shown in :ref:`dot file example`:
 .. code:: reST
    .. _dot file example:
    .. kernel-figure:: hello.dot
       :alt: hello world
       DOT's hello world example
 .. admonition:: hello.dot
    :class: rst-example
    .. _dot file example:
    .. kernel-figure:: hello.dot
       :alt: hello world
       DOT's hello world example
 ``kernel-render`` DOT
 ---------------------
 Embed *render* markups (or languages) like Graphviz's **DOT** is provided by the
 :ref:`linuxdoc:kernel-render` directive.  A simple example of embedded DOT_ is
 shown in figure :ref:`dot render example`:
 .. code:: reST
    .. _dot render example:
    .. kernel-render:: DOT
       :alt: digraph
       :caption: Embedded  DOT (Graphviz) code
       digraph foo {
         "bar" -> "baz";
       }
    Attribute ``caption`` is needed, if you want to refer the figure: :ref:`dot
    render example`.
 Please note :ref:`build tools <linuxdoc:kfigure_build_tools>`.  If Graphviz_ is
 installed, you will see an vector image.  If not, the raw markup is inserted as
 *literal-block*.
 .. admonition:: kernel-render DOT
    :class: rst-example
    .. _dot render example:
    .. kernel-render:: DOT
       :alt: digraph
       :caption: Embedded  DOT (Graphviz) code
       digraph foo {
         "bar" -> "baz";
       }
    Attribute ``caption`` is needed, if you want to refer the figure: :ref:`dot
    render example`.
 ``kernel-render`` SVG
 ---------------------
 A simple example of embedded SVG_ is shown in figure :ref:`svg render example`:
 .. code:: reST
    .. _svg render example:
    .. kernel-render:: SVG
       :caption: Embedded **SVG** markup
       :alt: so-nw-arrow
 ..
   .. code:: xml
       <?xml version="1.0" encoding="UTF-8"?>
       <svg xmlns="http://www.w3.org/2000/svg" version="1.1"
            baseProfile="full" width="70px" height="40px"
            viewBox="0 0 700 400"
            >
         <line x1="180" y1="370"
               x2="500" y2="50"
               stroke="black" stroke-width="15px"
               />
         <polygon points="585 0 525 25 585 50"
                  transform="rotate(135 525 25)"
                  />
       </svg>
 .. admonition:: kernel-render SVG
    :class: rst-example
    .. _svg render example:
    .. kernel-render:: SVG
       :caption: Embedded **SVG** markup
       :alt: so-nw-arrow
       <?xml version="1.0" encoding="UTF-8"?>
       <svg xmlns="http://www.w3.org/2000/svg" version="1.1"
            baseProfile="full" width="70px" height="40px"
            viewBox="0 0 700 400"
            >
         <line x1="180" y1="370"
               x2="500" y2="50"
               stroke="black" stroke-width="15px"
               />
         <polygon points="585 0 525 25 585 50"
                  transform="rotate(135 525 25)"
                  />
       </svg>
 .. _reST lists:
 List markups
 ============
 Bullet list
 -----------
 List markup (:duref:`ref <bullet-lists>`) is simple:
 .. code:: reST
    - This is a bulleted list.
 . Nested lists are possible, but be aware that they must be separated from
         the parent list items by blank line
 . Second item of nested list
    - It has two items, the second
      item uses two lines.
    #. This is a numbered list.
    #. It has two items too.
 .. admonition:: bullet list
    :class: rst-example
    - This is a bulleted list.
 . Nested lists are possible, but be aware that they must be separated from
         the parent list items by blank line
 . Second item of nested list
    - It has two items, the second
      item uses two lines.
    #. This is a numbered list.
    #. It has two items too.
 Horizontal list
 ---------------
 The :rst:dir:`.. hlist:: <hlist>` transforms a bullet list into a more compact
 list.
 .. code:: reST
    .. hlist::
       - first list item
       - second list item
       - third list item
       ...
 .. admonition:: hlist
    :class: rst-example
    .. hlist::
       - first list item
       - second list item
       - third list item
       - next list item
       - next list item xxxx
       - next list item yyyy
       - next list item zzzz
 Definition list
 ---------------
 .. sidebar:: Note ..
    - the term cannot have more than one line of text
    - there is **no blank line between term and definition block** // this
      distinguishes definition lists (:duref:`ref <definition-lists>`) from block
      quotes (:duref:`ref <block-quotes>`).
 Each definition list (:duref:`ref <definition-lists>`) item contains a term,
 optional classifiers and a definition.  A term is a simple one-line word or
 phrase.  Optional classifiers may follow the term on the same line, each after
 an inline ' : ' (**space, colon, space**).  A definition is a block indented
 relative to the term, and may contain multiple paragraphs and other body
 elements.  There may be no blank line between a term line and a definition block
 (*this distinguishes definition lists from block quotes*).  Blank lines are
 required before the first and after the last definition list item, but are
 optional in-between.
 Definition lists are created as follows:
 .. code:: reST
    term 1 (up to a line of text)
        Definition 1.
    See the typo : this line is not a term!
      And this is not term's definition.  **There is a blank line** in between
      the line above and this paragraph.  That's why this paragraph is taken as
      **block quote** (:duref:`ref <block-quotes>`) and not as term's definition!
    term 2
        Definition 2, paragraph 1.
        Definition 2, paragraph 2.
    term 3 : classifier
        Definition 3.
    term 4 : classifier one : classifier two
        Definition 4.
 .. admonition:: definition list
    :class: rst-example
    term 1 (up to a line of text)
        Definition 1.
    See the typo : this line is not a term!
      And this is not term's definition.  **There is a blank line** in between
      the line above and this paragraph.  That's why this paragraph is taken as
      **block quote** (:duref:`ref <block-quotes>`) and not as term's definition!
    term 2
        Definition 2, paragraph 1.
        Definition 2, paragraph 2.
    term 3 : classifier
        Definition 3.
    term 4 : classifier one : classifier two
 Quoted paragraphs
 -----------------
 Quoted paragraphs (:duref:`ref <block-quotes>`) are created by just indenting
 them more than the surrounding paragraphs.  Line blocks (:duref:`ref
 <line-blocks>`) are a way of preserving line breaks:
 .. code:: reST
    normal paragraph ...
    lorem ipsum.
       Quoted paragraph ...
       lorem ipsum.
    | These lines are
    | broken exactly like in
    | the source file.
 .. admonition:: Quoted paragraph and line block
    :class: rst-example
    normal paragraph ...
    lorem ipsum.
       Quoted paragraph ...
       lorem ipsum.
    | These lines are
    | broken exactly like in
    | the source file.
 .. _reST field list:
 Field Lists
 -----------
 .. _Sphinx Field Lists:
    https://www.sphinx-doc.org/en/master/usage/restructuredtext/field-lists.html
 .. sidebar::  bibliographic fields
    First lines fields are bibliographic fields, see `Sphinx Field Lists`_.
 Field lists are used as part of an extension syntax, such as options for
 directives, or database-like records meant for further processing.  Field lists
 are mappings from field names to field bodies.  They marked up like this:
 .. code:: reST
    :fieldname: Field content
    :foo:       first paragraph in field foo
                second paragraph in field foo
    :bar:       Field content
 .. admonition:: Field List
    :class: rst-example
    :fieldname: Field content
    :foo:       first paragraph in field foo
                second paragraph in field foo
    :bar:       Field content
 They are commonly used in Python documentation:
 .. code:: python
    def my_function(my_arg, my_other_arg):
        """A function just for me.
        :param my_arg: The first of my arguments.
        :param my_other_arg: The second of my arguments.
        :returns: A message (just for me, of course).
        """
 Further list blocks
 -------------------
 - field lists (:duref:`ref <field-lists>`, with caveats noted in
   :ref:`reST field list`)
 - option lists (:duref:`ref <option-lists>`)
 - quoted literal blocks (:duref:`ref <quoted-literal-blocks>`)
 - doctest blocks (:duref:`ref <doctest-blocks>`)
 Admonitions
 ===========
 Sidebar
 -------
 Sidebar is an eye catcher, often used for admonitions pointing further stuff or
 site effects.  Here is the source of the sidebar :ref:`on top of this page <reST
 primer>`.
 .. code:: reST
    .. sidebar:: KISS_ and readability_
       Instead of defining more and more roles, we at searx encourage our
       contributors to follow principles like KISS_ and readability_.
 Generic admonition
 ------------------
 The generic :dudir:`admonition <admonitions>` needs a title:
 .. code:: reST
    .. admonition:: generic admonition title
       lorem ipsum ..
 .. admonition:: generic admonition title
    lorem ipsum ..
 Specific admonitions
 --------------------
 Specific admonitions: :dudir:`hint`, :dudir:`note`, :dudir:`tip` :dudir:`attention`,
 :dudir:`caution`, :dudir:`danger`, :dudir:`error`, , :dudir:`important`, and
 :dudir:`warning` .
 .. code:: reST
    .. hint::
       lorem ipsum ..
    .. note::
       lorem ipsum ..
    .. warning::
       lorem ipsum ..
 .. hint::
    lorem ipsum ..
 .. note::
    lorem ipsum ..
 .. tip::
    lorem ipsum ..
 .. attention::
    lorem ipsum ..
 .. caution::
    lorem ipsum ..
 .. danger::
    lorem ipsum ..
 .. important::
    lorem ipsum ..
 .. error::
    lorem ipsum ..
 .. warning::
    lorem ipsum ..
 Tables
 ======
 .. sidebar:: Nested tables
    Nested tables are ugly! Not all builder support nested tables, don't use
    them!
 ASCII-art tables like :ref:`reST simple table` and :ref:`reST grid table` might
 be comfortable for readers of the text-files, but they have huge disadvantages
 in the creation and modifying.  First, they are hard to edit.  Think about
 adding a row or a column to a ASCII-art table or adding a paragraph in a cell,
 it is a nightmare on big tables.
 .. sidebar:: List tables
    For meaningful patch and diff use :ref:`reST flat table`.
 Second the diff of modifying ASCII-art tables is not meaningful, e.g. widening a
 cell generates a diff in which also changes are included, which are only
 ascribable to the ASCII-art.  Anyway, if you prefer ASCII-art for any reason,
 here are some helpers:
 * `Emacs Table Mode`_
 * `Online Tables Generator`_
 .. _reST simple table:
 Simple tables
 -------------
 :duref:`Simple tables <simple-tables>` allow *colspan* but not *rowspan*.  If
 your table need some metadata (e.g. a title) you need to add the ``.. table::
 directive`` :dudir:`(ref) <table>` in front and place the table in its body:
 .. code:: reST
    .. table:: foo gate truth table
       :widths: grid
       :align: left
       ====== ====== ======
           Inputs    Output
       ------------- ------
       A      B      A or B
       ====== ====== ======
       False
       --------------------
       True
       --------------------
       True   False  True
              (foo)
       ------ ------ ------
       False  True
              (foo)
       ====== =============
 .. admonition:: Simple ASCII table
    :class: rst-example
    .. table:: foo gate truth table
       :widths: grid
       :align: left
       ====== ====== ======
           Inputs    Output
       ------------- ------
       A      B      A or B
       ====== ====== ======
       False
       --------------------
       True
       --------------------
       True   False  True
              (foo)
       ------ ------ ------
       False  True
              (foo)
       ====== =============
 .. _reST grid table:
 Grid tables
 -----------
 :duref:`Grid tables <grid-tables>` allow colspan *colspan* and *rowspan*:
 .. code:: reST
    .. table:: grid table example
       :widths: 1 1 5
       +------------+------------+-----------+
       | Header 1   | Header 2   | Header 3  |
       +============+============+===========+
       | body row 1 | column 2   | column 3  |
       +------------+------------+-----------+
       | body row 2 | Cells may span columns.|
       +------------+------------+-----------+
       | body row 3 | Cells may  | - Cells   |
       +------------+ span rows. | - contain |
       | body row 4 |            | - blocks. |
       +------------+------------+-----------+
 .. admonition:: ASCII grid table
    :class: rst-example
    .. table:: grid table example
       :widths: 1 1 5
       +------------+------------+-----------+
       | Header 1   | Header 2   | Header 3  |
       +============+============+===========+
       | body row 1 | column 2   | column 3  |
       +------------+------------+-----------+
       | body row 2 | Cells may span columns.|
       +------------+------------+-----------+
       | body row 3 | Cells may  | - Cells   |
       +------------+ span rows. | - contain |
       | body row 4 |            | - blocks. |
       +------------+------------+-----------+
 .. _reST flat table:
 flat-table
 ----------
 The ``flat-table`` is a further developed variant of the :ref:`list tables
 <linuxdoc:list-table-directives>`.  It is a double-stage list similar to the
 :dudir:`list-table` with some additional features:
 column-span: ``cspan``
   with the role ``cspan`` a cell can be extended through additional columns
 row-span: ``rspan``
   with the role ``rspan`` a cell can be extended through additional rows
 auto-span:
   spans rightmost cell of a table row over the missing cells on the right side
   of that table-row.  With Option ``:fill-cells:`` this behavior can changed
   from *auto span* to *auto fill*, which automatically inserts (empty) cells
   instead of spanning the last cell.
 options:
   :header-rows:   [int] count of header rows
   :stub-columns:  [int] count of stub columns
   :widths:        [[int] [int] ... ] widths of columns
   :fill-cells:    instead of auto-span missing cells, insert missing cells
 roles:
   :cspan: [int] additional columns (*morecols*)
   :rspan: [int] additional rows (*morerows*)
 The example below shows how to use this markup.  The first level of the staged
 list is the *table-row*. In the *table-row* there is only one markup allowed,
 the list of the cells in this *table-row*. Exception are *comments* ( ``..`` )
 and *targets* (e.g. a ref to :ref:`row 2 of table's body <row body 2>`).
 .. code:: reST
    .. flat-table:: ``flat-table`` example
       :header-rows: 2
       :stub-columns: 1
       :widths: 1 1 1 1 2
       * - :rspan:`1` head / stub
         - :cspan:`3` head 1.1-4
       * - head 2.1
         - head 2.2
         - head 2.3
         - head 2.4
       * .. row body 1 / this is a comment
         - row 1
         - :rspan:`2` cell 1-3.1
         - cell 1.2
         - cell 1.3
         - cell 1.4
       * .. Comments and targets are allowed on *table-row* stage.
         .. _`row body 2`:
         - row 2
         - cell 2.2
         - :rspan:`1` :cspan:`1`
           cell 2.3 with a span over
           * col 3-4 &
           * row 2-3
       * - row 3
         - cell 3.2
       * - row 4
         - cell 4.1
         - cell 4.2
         - cell 4.3
         - cell 4.4
       * - row 5
         - cell 5.1 with automatic span to rigth end
       * - row 6
         - cell 6.1
         - ..
 .. admonition:: List table
    :class: rst-example
    .. flat-table:: ``flat-table`` example
       :header-rows: 2
       :stub-columns: 1
       :widths: 1 1 1 1 2
       * - :rspan:`1` head / stub
         - :cspan:`3` head 1.1-4
       * - head 2.1
         - head 2.2
         - head 2.3
         - head 2.4
       * .. row body 1 / this is a comment
         - row 1
         - :rspan:`2` cell 1-3.1
         - cell 1.2
         - cell 1.3
         - cell 1.4
       * .. Comments and targets are allowed on *table-row* stage.
         .. _`row body 2`:
         - row 2
         - cell 2.2
         - :rspan:`1` :cspan:`1`
           cell 2.3 with a span over
           * col 3-4 &
           * row 2-3
       * - row 3
         - cell 3.2
       * - row 4
         - cell 4.1
         - cell 4.2
         - cell 4.3
         - cell 4.4
       * - row 5
         - cell 5.1 with automatic span to rigth end
       * - row 6
         - cell 6.1
         - ..
 CSV table
 ---------
 CSV table might be the choice if you want to include CSV-data from a outstanding
 (build) process into your documentation.
 .. code:: reST
    .. csv-table:: CSV table example
       :header: .. , Column 1, Column 2
       :widths: 2 5 5
       :stub-columns: 1
       :file: csv_table.txt
 Content of file ``csv_table.txt``:
 .. literalinclude:: csv_table.txt
 .. admonition:: CSV table
    :class: rst-example
    .. csv-table:: CSV table example
       :header: .. , Column 1, Column 2
       :widths: 3 5 5
       :stub-columns: 1
       :file: csv_table.txt
 Templating
 ==========
 .. sidebar:: Build environment
    All *generic-doc* tasks are running in the :ref:`build environment <make
    pyenv>`.
 Templating is suitable for documentation which is created generic at the build
 time.  The sphinx-jinja_ extension evaluates jinja_ templates in the :ref:`build
 environment <make pyenv>` (with searx modules installed).  We use this e.g. to
 build chapter: :ref:`engines generic`.  Below the jinja directive from the
 :origin:`docs/admin/engines.rst` is shown:
 .. literalinclude:: ../admin/engines.rst
    :language: reST
    :start-after: .. _configured engines:
 The context for the template is selected in the line ``.. jinja:: webapp``.  In
 sphinx's build configuration (:origin:`docs/conf.py`) the ``webapp`` context
 points to the name space of the python module: ``webapp``.
 .. code:: py
    from searx import webapp
    jinja_contexts = {
        'webapp': dict(**webapp.__dict__)
    }
 Tabbed views
 ============
 .. _sphinx-tabs: https://github.com/djungelorm/sphinx-tabs
 .. _basic-tabs: https://github.com/djungelorm/sphinx-tabs#basic-tabs
 .. _group-tabs: https://github.com/djungelorm/sphinx-tabs#group-tabs
 .. _code-tabs: https://github.com/djungelorm/sphinx-tabs#code-tabs
 With `sphinx-tabs`_ extension we have *tabbed views*.  To provide installation
 instructions with one tab per distribution we use the `group-tabs`_ directive,
 others are basic-tabs_ and code-tabs_.  Below a *group-tab* example from
 :ref:`docs build` is shown:
 .. literalinclude:: ../admin/buildhosts.rst
    :language: reST
    :start-after: .. SNIP sh lint requirements
    :end-before: .. SNAP sh lint requirements
 .. _math:
 Math equations
 ==============
 .. _Mathematics: https://en.wikibooks.org/wiki/LaTeX/Mathematics
 .. _amsmath user guide:
    http://vesta.informatik.rwth-aachen.de/ftp/pub/mirror/ctan/macros/latex/required/amsmath/amsldoc.pdf
 .. sidebar:: About LaTeX
    - `amsmath user guide`_
    - Mathematics_
    - :ref:`docs build`
 The input language for mathematics is LaTeX markup using the :ctan:`amsmath`
 package.
 To embed LaTeX markup in reST documents, use role :rst:role:`:math: <math>` for
 inline and directive :rst:dir:`.. math:: <math>` for block markup.
 .. code:: reST
    In :math:numref:`schroedinger general` the time-dependent Schrödinger equation
    is shown.
    .. math::
       :label: schroedinger general
        \mathrm{i}\hbar\dfrac{\partial}{\partial t} |\,\psi (t) \rangle =
              \hat{H} |\,\psi (t) \rangle.
 .. admonition:: LaTeX math equation
    :class: rst-example
    In :math:numref:`schroedinger general` the time-dependent Schrödinger equation
    is shown.
    .. math::
       :label: schroedinger general
        \mathrm{i}\hbar\dfrac{\partial}{\partial t} |\,\psi (t) \rangle =
              \hat{H} |\,\psi (t) \rangle.
 The next example shows the difference of ``\tfrac`` (*textstyle*) and ``\dfrac``
 (*displaystyle*) used in a inline markup or another fraction.
 .. code:: reST
    ``\tfrac`` **inline example** :math:`\tfrac{\tfrac{1}{x}+\tfrac{1}{y}}{y-z}`
    ``\dfrac`` **inline example** :math:`\dfrac{\dfrac{1}{x}+\dfrac{1}{y}}{y-z}`
 .. admonition:: Line spacing
    :class: rst-example
    Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
    eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam
    voluptua.  ...
    ``\tfrac`` **inline example** :math:`\tfrac{\tfrac{1}{x}+\tfrac{1}{y}}{y-z}`
    At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd
    gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.
    Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy
    eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam
    voluptua.  ...
    ``\tfrac`` **inline example** :math:`\dfrac{\dfrac{1}{x}+\dfrac{1}{y}}{y-z}`
    At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd
    gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.
 .. _KISS: https://en.wikipedia.org/wiki/KISS_principle
 .. _readability: https://docs.python-guide.org/writing/style/
 .. _Sphinx-Primer:
     http://www.sphinx-doc.org/en/master/usage/restructuredtext/basics.html
 .. _reST: https://docutils.sourceforge.io/rst.html
 .. _Sphinx Roles:
     https://www.sphinx-doc.org/en/master/usage/restructuredtext/roles.html
 .. _Sphinx: http://www.sphinx-doc.org
 .. _`sphinx-doc FAQ`: http://www.sphinx-doc.org/en/stable/faq.html
 .. _Sphinx markup constructs:
     http://www.sphinx-doc.org/en/stable/markup/index.html
 .. _`sphinx cross references`:
     http://www.sphinx-doc.org/en/stable/markup/inline.html#cross-referencing-arbitrary-locations
 .. _sphinx.ext.extlinks:
     https://www.sphinx-doc.org/en/master/usage/extensions/extlinks.html
 .. _intersphinx: http://www.sphinx-doc.org/en/stable/ext/intersphinx.html
 .. _sphinx config: http://www.sphinx-doc.org/en/stable/config.html
 .. _Sphinx's autodoc: http://www.sphinx-doc.org/en/stable/ext/autodoc.html
 .. _Sphinx's Python domain:
     http://www.sphinx-doc.org/en/stable/domains.html#the-python-domain
 .. _Sphinx's C domain:
    http://www.sphinx-doc.org/en/stable/domains.html#cross-referencing-c-constructs
 .. _doctree:
     http://www.sphinx-doc.org/en/master/extdev/tutorial.html?highlight=doctree#build-phases
 .. _docutils: http://docutils.sourceforge.net/docs/index.html
 .. _docutils FAQ: http://docutils.sourceforge.net/FAQ.html
 .. _linuxdoc: https://return42.github.io/linuxdoc
 .. _jinja: https://jinja.palletsprojects.com/
 .. _sphinx-jinja: https://github.com/tardyp/sphinx-jinja
 .. _SVG: https://www.w3.org/TR/SVG11/expanded-toc.html
 .. _DOT: https://graphviz.gitlab.io/_pages/doc/info/lang.html
 .. _`Graphviz's dot`: https://graphviz.gitlab.io/_pages/pdf/dotguide.pdf
 .. _Graphviz: https://graphviz.gitlab.io
 .. _ImageMagick: https://www.imagemagick.org
 .. _`Emacs Table Mode`: https://www.emacswiki.org/emacs/TableMode
 .. _`Online Tables Generator`: http://www.tablesgenerator.com/text_tables
 .. _`OASIS XML Exchange Table Model`: https://www.oasis-open.org/specs/tm9901.html